Full length and circumferential dimensional measurement of tubular goods, and storage of the numerical results in a data base array maintaining an association between each circumferential plane of data and its longitudinal position, represents the state of the art in tubular good inspection systems. A goal of such systems is to use the data to reconstruct a virtual three-dimensional representation of a tubular good, including off-axis deviations along its length. Typical state-of-the-art tubular good inspection systems directed to this goal presently use ultrasonic testing (UT) means to measure wall thickness dimensions, combined with laser or light emitting apparatus to measure the associated outer diameters. Those current systems, however, do not capture off-axis deviations from the baseline longitudinal straightness of the tubular good.
Such data arrays of wall thickness and associated outer diameter measurements produce pseudo (virtual) three-dimensional representations of short (typically one-half inch) sections of a pipe or other tubular good at discrete longitudinal positions. Each adjacent ring section is characterized by its own independent, discrete set of three-dimensional data, and the only relative measure between adjacent discrete sections is the longitudinal distance between them. When data of this sort is graphically displayed, with all discrete ring sections connected, a perfectly straight three-dimensional representation of a tubular good is produced. In other words, the geometric centerlines of the discrete ring sections align themselves along the longitudinal z-axis and do not deviate radially in the transverse x-y plane.
Manufactured pipes, however, are never perfectly straight and have sections that are radially offset in the transverse x-y plane. When the geometric centers of each section of a manufactured pipe are measured and displayed graphically, off-axis hooks (end area deviations), sweeps (full length bows), and helical out-of-straightness patterns are often observed. The tubular good dimensional measurement systems in use today do not address the off-axis relational data that is needed to produce true three-dimensional representations of manufactured pipes, which exhibit complex off-axis straightness imperfections.
The cost to inspect pipe, for example, with the intent of capturing wall thickness and associated outside diameter dimensions is a function of several factors, including the cost of the measurement apparatus, the cost of the systems used to store and process the generated data arrays for each pipe, the time required to complete the full inspection process, the manpower and training required to operate the systems, and the cost to maintain the measurement system and the data storage and processing system. Typical retail prices for inspecting a small quantity of pipe range from $900 to $1,200 per joint of oil country tubular casing. Large quantity retail prices are approximately $300 per joint. Wth respect to maintenance, ultrasonic inspection facilities with large transducer arrays are typically employed to measure oil country tubular goods, which significantly increases maintenance costs. Inspection costs can significantly increase the cost of tubular goods.
In the oil drilling industry, mechanical, multi-arm, spider-like devices are used to physically measure and log the inside diameters of a tubular good along its entire length. In other industries, such as the defense industry, laser measurement systems are used to measure the inside diameter of a tubular artillery canon barrel along its entire length. Each of these systems is far less expensive than a full length ultrasonic wall measurement system and can complete a full length inspection in a fraction of the time. Each such system, however, is not able to address the drawbacks of conventional systems which do not capture off-axis deviations from a base line of true straightness or, in some cases, the other remaining tubular dimensions.